Oh gosh I would have to say that I dislike endings, I try to avoid them at all costs. All the anime that I've seen [Which is a lot] have in my opinion horrible endings! But, if I was to choose some that haven't scarred me with either a cliffhanger ending, or a annyoing conclusion, or just a happy ending I was hoping for I would have to say animes with sad endings like: Dog of Flanders cried so much, Grave of the Fire flies cried so much, Code Code Geass, Sailor Moon becasue I was like WTF was that NOOOO can't be the end cried so much!!! I suppose I'm pessimistic lol

The ending of Welcome to the NHK!
"It's not just dramatic! IT'S FUCKING DRAMATIC!!"

I can't agree more! Welcome to the NHK deserves more content (at least the anime does, not sure if the manga/novels have more content after the anime ended or not).

The Manga and Novel do have more story, but they are several differences between the anime and each other. One of which is that Sato is a drug addict, rather than just insane. But yeah, I believe the manga is the longest, with the end of the anime being somewhere around the mid-point.

From TvTropes:

The book, manga and anime are each rather different in both story and themes. The anime and manga follow essentially the same plot until the manga's divergence from the novel, leading to its own, separate conclusion. The novel tends to be somewhat darker, focusing more on the characters' issues and less on the love story, which is essentially the focus of the anime, with the manga somewhere in between. There are significant differences in the specific way some events happen in the anime and manga, even when they're otherwise almost identical, which tends to bring out the change in tone. Many events of the novel (the fight scene, the visit to the church) never occur in the anime or manga, and vice versa (the "summer vacation", the entire second half of the manga).

I kinda figured. I really need to go back and read the manga, because it's my one of my favorite anime of all time.

cowboy bebop's ending is very tragic and I still find it hard to watch even though I have watched the series dozens of times.
angel beats also had a very emotional ending that pulled on the heartstrings.
not exactly an ending but the second to last episode of 11eyes was very powerful.

these are my top three although if I thought hard enough I could probably come up with some others

Most endings affect me because I hate when my journey with a certain group of characters comes to an end.. Whether it's in an anime, book, or video game. The first one that instantly popped into my head anime-wise was Nana.